Function shadow_topk 

pub fn shadow_topk() -> usize

2026-09-25: METRALE_MTP_SHADOW_TOPK=k: log the drafter’s top-k candidates at each draft position, and the verify steps’ target tokens, without changing token selection. 0 (unset or unparseable) is off; k is capped at 8. ModelLevers::shadow_topk and SchedLevers::shadow_topk both read it here, once per run.